Model approach to the analysis of effects of modulated electromagnetic radiation on animal cells

Frequency-dependent modifications of intracellular free calcium concentrati on ([Ca2+](i)) in neutrophils exposured to modulated extremely high frequen cy electromagnetic radiation were analysed using a special mathematical mod el for [Ca2+](i) oscillations. The model took into account the activation o f Ca2+ influx into the cell by cytosolic Ca2+ and Ca2+-induced Ca2+ release from intracellular stores. The calcium channels of plasma membrane were ch osen as a target for the influence of harmonic signal and additive noise in the model. The model simulation showed that in response to modulating sign al, the rise in [Ca2+], has frequency dependence and phase dependence in re lation to the moment of chemical stimulation. The phase-frequency dependenc e of the effect was observed at a certain sequence of delivery of chemical stimulus and modulating signal to the cell. At intensities of modulating si gnals exceeding the threshold, a rise in [Ca2+](i), reaching a level of mor e than 50% of the initial level, was observed at a frequency of about 1 Hz and in the phase range of 0.3-2.5 radians. The effect was found only at hig h intensities of chemical stimulus. The additive noise introduced into the system modified qualitatively and quantitatively the phase-frequency charac teristics of the cell response to the modulating signal. An increase in noi se intensity resulted in a displacement of the average frequency of the ban d bf rise in [Ca2+](i) and then the emergence of a set of bands with a grea ter Q-factors. The analysis of dynamics of the nonlinear system in terms of the stability theory showed that, as the intensity of chemical stimulus in creases, the system transits by means of a series of bifurcations from regu lar driving to chaotic, and then to oscillations, induced by a modulating h armonic signal. The boundary of the transition of oscillations from chaotic to induced ones corresponds to a specific <<threshold>> of the intensity o f chemical stimulus for the significant rise in [Ca2+](i) in response to th e modulating signal. The results of the model analysis are in good correspo ndence with the experimental data obtained earlier, namely, with the effect s of modulated extremely high-frequency electromagnetic radiation on neutro phils, which were observed only in the presence of Ca2+ in extracellular me dium and at high concentrations of calcium ionophore A23187. Thus, as the c haracteristic frequency of the quasiperiodic process of calcium signalling in the cell coincides with the frequency of external field, a narrow-band r ise in [Ca2+](i) is observed, which can result in a modification of the fun ctional activity of the cell.